The present invention relates to a testing head for microstructures, and, more particularly, the invention relates to a testing head for use on semiconductor integrated devices, and a method of making the microstructure testing heads.
A testing head is essentially a device adapted to electrically interconnect a number of contact pads of a microstructure with corresponding paths of a measuring machine employed to carry out the testing.
The circuit testing procedure is used to detect any faulty integrated circuits directly at the manufacturing stage of the circuits. Testing heads are generally employed to electrically test the integrated circuits on the wafer itself before the circuits are separated and inserted into a chip package.
A testing head comprises one or more pairs of parallel guide plates placed a given distance apart (to leave an air space therebetween), and a set of special movable contact elements. The pair of guide plates consists of a top guide plate and a bottom guide plate, both of which are formed with guide holes for the movable contact elements to be passed therethrough. The individual contact elements are typically small wires made of special alloys with good electrical and mechanical properties. These contact elements will be referred to as xe2x80x9cprobesxe2x80x9d or xe2x80x9ccontact probesxe2x80x9d through the remainder of this specification, to highlight the function that they serve.
A good contact between the probes and the contact pads of a device under test is achieved by keeping the testing head pressed against the device, with the probes bending or flexing in the air gap between the guide plates. Testing heads of this type are commonly known as xe2x80x9cvertical probesxe2x80x9d.
The amount of bending undergone by the probes, and the force required to produce the bending, is related to a number of factors, including the physical characteristics of the alloy used to make the probes, and an amount of offset between the guide holes in the top plate and the corresponding guide holes in the bottom plate, as well as other factors.
Excessive bending of the probes should be avoided, however, because a probe may be flexed too much and not return to its original shape, or may otherwise become stuck in the guide holes.
It should be noted that, for the testing head to perform satisfactorily, the probes must be allowed an amount of axial play in the guide holes. Thus, if a single probe breaks, the broken probe can be removed and replaced, without the need to replace the entire testing head.
These factors should be taken into account when manufacturing the testing head, because a good electric connection between the probes and the device under test is mandatory.
In some cases, the contact probes are affixed to the top guide plate of the testing head in a permanent manner. This is known as a clamped probe testing head. However, testing heads with loose-mounted probes are more frequently used, where the probes are electrically connected to a xe2x80x9cboardxe2x80x9d by a microcontact interface called the xe2x80x9cspace transformerxe2x80x9d. This is known as a loose probe testing head.
In the latter case, each contact probe has a second contacting tip opposite the one used to contact the device under test. This second contacting tip is aimed at one of the contact pads on the space transformer. A good electric contact is established between the probes and the space transformer in a similar way as the contact to the device being tested, i.e., by pressing the probes against the contact pads on the space transformer.
One advantage of a loose probe testing head is that one or more faulty probes, or the whole set of probes, can be replaced with greater ease than if clamped probe testing heads are used.
However, the top and bottom guide plates must be designed to hold the contact probes in place, even when no device is abutting their contacting tips for testing, or when the whole set of probes is moved during a replacement operation.
Embodiments of the invention provide a testing head for microstructures that makes firm electric contact with a device under test, holds the probes securely in their guides, and minimizes the likelihood of bent probes becoming stuck in their guides.
Presented is a device that has contact probes whose contacting tips meet the contact pads under a non-zero pitch angle and scrub their surfaces the moment a device to be tested is drawn against the contacting tips, thereby causing the contact probes to bend within an air gap. Additionally presented is a method of creating an electro/mechanical connection between a microstructure testing head and a device to be tested.
The features and advantages of a testing head according to the invention will be apparent from the following description of embodiments thereof, given by way of non-limiting examples with reference to the accompanying drawings.